(1) Field of the Invention:
The present invention relates to a magnetic recording medium. More particularly, the present invention relates to a magnetic recording medium having excellent durability.
(2) Description of the Prior Art:
A magnetic recording medium is generally prepared by coating a substrate such as a polyester film with a magnetic paint comprising a magnetic powder, a binder resin, an organic solvent and other necessary ingredients. A magnetic recording medium having reduced friction of a magnetic layer and excellent durability is especially required for a floppy disk because the magnetic layer of a disk is likely to wear away by contact with a magnetic head or jacket liner during the production or reproduction processes.
A known process for improving the wear resistance of the magnetic layer comprises incorporation of various lubricants in the magnetic layer.
Various compounds have been proposed as the lubricant, for example, fatty acids, fatty acid esters, fatty acid amides, liquid paraffins and waxes. However, the performance of these lubricants are unsatisfactory, especially in single use. For example, even if the durability is effectively improved, the compatibility with the resin binder is poor and bleeding of the lubricant from the surface of the magnetic layer often occurs, or even though bleeding is prevented, the improvement of the durability is insufficient.
Accordingly, some of the foregoing compounds are sometimes practically used in combination, but at the present, no sufficiently satisfactory lubricant system is obtained.
Carbon black is often incorporated into a magnetic layer of a magnetic recording medium such as a floppy disk. It is considered that the primary objects of incorporation of carbon black are to prevent accumulation of static charges in the magnetic layer and to impart a required light-shielding property to the magnetic recording medium.
Several carbon black blend systems have been proposed for these objects.
According to the inventors' investigations, it was confirmed that when a kind of carbon black is changed, also the durability of the magnetic recording medium is sometimes changed, and when a combination of a carbon black and a compound to be incorporated as lubricant is changed, the durability can be changed.
The inventors made a further research based on the above findings for the purpose of improving the durability of the magnetic recording medium.
Moreover, since a device equipped with a magnetic recording medium such as a floppy disk is often used outdoors recently, an excellent durable magnetic recording medium is eagerly desired.